/*-------------------------------------------------------------------------
 
  LargeObject.cs
      This class is a port of the class LargeObject.java implemented by 
      PostgreSQL Global Development Group
 
  Copyright (c) 2004, Emiliano Necciari
  Original Code: Copyright (c) 2003, PostgreSQL Global Development Group
  
  Note: (Francisco Figueiredo Jr.)
  	Changed case of method names to conform to .Net names standard.
  	Also changed type names to their true names. i.e. int -> Int32
 
// Permission to use, copy, modify, and distribute this software and its
// documentation for any purpose, without fee, and without a written
// agreement is hereby granted, provided that the above copyright notice
// and this paragraph and the following two paragraphs appear in all copies.
// 
// IN NO EVENT SHALL THE NPGSQL DEVELOPMENT TEAM BE LIABLE TO ANY PARTY
// FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
// INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
// DOCUMENTATION, EVEN IF THE NPGSQL DEVELOPMENT TEAM HAS BEEN ADVISED OF
// THE POSSIBILITY OF SUCH DAMAGE.
// 
// THE NPGSQL DEVELOPMENT TEAM SPECIFICALLY DISCLAIMS ANY WARRANTIES,
// INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
// ON AN "AS IS" BASIS, AND THE NPGSQL DEVELOPMENT TEAM HAS NO OBLIGATIONS
// TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
-------------------------------------------------------------------------
*/

using System;

namespace NpgsqlTypes
{
	public class LargeObject
	{
		/*
         * Indicates a seek from the begining of a file
         */
		public const Int32 SEEK_SET = 0;

		/*
         * Indicates a seek from the current position
         */
		public const Int32 SEEK_CUR = 1;

		/*
         * Indicates a seek from the end of a file
         */
		public const Int32 SEEK_END = 2;

		private readonly Fastpath fp; // Fastpath API to use
		private readonly Int32 oid; // OID of this object
		private readonly Int32 fd; // the descriptor of the open large object

		private Boolean closed = false; // true when we are closed

		/*
         * This opens a large object.
         *
         * <p>If the object does not exist, then an NpgsqlException is thrown.
         *
         * @param fp FastPath API for the connection to use
         * @param oid of the Large Object to open
         * @param mode Mode of opening the large object
         * (defined in LargeObjectManager)
         * @exception NpgsqlException if a database-access error occurs.
         * @see org.postgresql.largeobject.LargeObjectManager
         */

		public LargeObject(Fastpath fp, Int32 oid, Int32 mode)
		{
			this.fp = fp;
			this.oid = oid;

			FastpathArg[] args = new FastpathArg[2];
			args[0] = new FastpathArg(oid);
			args[1] = new FastpathArg(mode);
			this.fd = fp.GetInteger("lo_open", args);
		}


		/*
         * @return the OID of this LargeObject
         */

		public Int32 GetOID()
		{
			return oid;
		}

		/*
         * This method closes the object. You must not call methods in this
         * object after this is called.
         * @exception NpgsqlException if a database-access error occurs.
         */

		public void Close()
		{
			if (!closed)
			{
				// finally close
				FastpathArg[] args = new FastpathArg[1];
				args[0] = new FastpathArg(fd);
				fp.FastpathCall("lo_close", false, args); // true here as we dont care!!
				closed = true;
			}
		}

		/*
         * Reads some data from the object, and return as a byte[] array
         *
         * @param len number of bytes to read
         * @return byte[] array containing data read
         * @exception NpgsqlException if a database-access error occurs.
         */

		public Byte[] Read(Int32 len)
		{
			// This is the original method, where the entire block (len bytes)
			// is retrieved in one go.
			FastpathArg[] args = new FastpathArg[2];
			args[0] = new FastpathArg(fd);
			args[1] = new FastpathArg(len);
			return fp.GetData("loread", args);

			// This version allows us to break this down Int32o 4k blocks
			//if (len<=4048) {
			//// handle as before, return the whole block in one go
			//FastpathArg args[] = new FastpathArg[2];
			//args[0] = new FastpathArg(fd);
			//args[1] = new FastpathArg(len);
			//return fp.getData("loread",args);
			//} else {
			//// return in 4k blocks
			//byte[] buf=new byte[len];
			//int off=0;
			//while (len>0) {
			//int bs=4048;
			//len-=bs;
			//if (len<0) {
			//bs+=len;
			//len=0;
			//}
			//read(buf,off,bs);
			//off+=bs;
			//}
			//return buf;
			//}
		}

		/*
         * Reads some data from the object into an existing array
         *
         * @param buf destination array
         * @param off offset within array
         * @param len number of bytes to read
         * @return the number of bytes actually read
         * @exception NpgsqlException if a database-access error occurs.
         */

		public Int32 Read(Byte[] buf, Int32 off, Int32 len)
		{
			Byte[] b = Read(len);
			if (b.Length < len)
			{
				len = b.Length;
			}
			Array.Copy(b, 0, buf, off, len);
			return len;
		}

		/*
         * Writes an array to the object
         *
         * @param buf array to write
         * @exception NpgsqlException if a database-access error occurs.
         */

		public void Write(Byte[] buf)
		{
			FastpathArg[] args = new FastpathArg[2];
			args[0] = new FastpathArg(fd);
			args[1] = new FastpathArg(buf);
			fp.FastpathCall("lowrite", false, args);
		}

		/*
         * Writes some data from an array to the object
         *
         * @param buf destination array
         * @param off offset within array
         * @param len number of bytes to write
         * @exception NpgsqlException if a database-access error occurs.
         */

		public void Write(Byte[] buf, Int32 off, Int32 len)
		{
			Byte[] data = new Byte[len];

			Array.Copy(buf, off, data, 0, len);
			Write(data);
		}

		/*
         * Sets the current position within the object.
         *
         * <p>This is similar to the fseek() call in the standard C library. It
         * allows you to have random access to the large object.
         *
         * @param pos position within object
         * @param ref Either SEEK_SET, SEEK_CUR or SEEK_END
         * @exception NpgsqlException if a database-access error occurs.
         */

		public void Seek(Int32 pos, Int32 refi)
		{
			FastpathArg[] args = new FastpathArg[3];
			args[0] = new FastpathArg(fd);
			args[1] = new FastpathArg(pos);
			args[2] = new FastpathArg(refi);
			fp.FastpathCall("lo_lseek", false, args);
		}

		/*
         * Sets the current position within the object.
         *
         * <p>This is similar to the fseek() call in the standard C library. It
         * allows you to have random access to the large object.
         *
         * @param pos position within object from begining
         * @exception NpgsqlException if a database-access error occurs.
         */

		public void Seek(Int32 pos)
		{
			Seek(pos, SEEK_SET);
		}

		/*
         * @return the current position within the object
         * @exception NpgsqlException if a database-access error occurs.
         */

		public Int32 Tell()
		{
			FastpathArg[] args = new FastpathArg[1];
			args[0] = new FastpathArg(fd);
			return fp.GetInteger("lo_tell", args);
		}

		/*
         * This method is inefficient, as the only way to find out the size of
         * the object is to seek to the end, record the current position, then
         * return to the original position.
         *
         * <p>A better method will be found in the future.
         *
         * @return the size of the large object
         * @exception NpgsqlException if a database-access error occurs.
         */

		public Int32 Size()
		{
			Int32 cp = Tell();
			Seek(0, SEEK_END);
			Int32 sz = Tell();
			Seek(cp, SEEK_SET);
			return sz;
		}
	}
}